1. Field of the Invention
This invention generally relates to printers of the type which print characters in the form of dot matrix, and, in particular, to a system for controlling the printing of a continuous vertical line in such printers. More specifically, the present invention relates to a printer, such as a thermal line printer, which is capable of printing characters in the form of dot matrix with a plurality of different kinds of fonts different in size, in particular vertical length.
2. Description of the Prior Art
Recently, there has been developed a terminal having both a document creating and editing function and a communicating function, such as a communication wordprocessor and a wordprocessor capable of carrying out international communication. In such communication wordprocessors, especially those capable of carrying out international communication, printers to be used for printing document information are often required to be variable in print pitch, or character spacing. Typically, there are three print pitches: print pitch 10--10 characters per inch; print pitch 12--12 characters per inch; and print pitch 15--15 characters per inch, and printers to be used with internationally communicatable wordprocessors are usually required to be operable selectively at one of these three print pitches. In such a case, printers must be provided with three fonts different in size vertically as well as horizontally.
Under the circumstances, there has been proposed a thermal line printer capable of printing characters with one of a plurality of different fonts selectively. In such a thermal line printer, however, in the case of printing vertical lines, for example, in forming a table, if fonts differ between the two consecutive print lines as changed from a lower pitch to a higher pitch, for example from print pitch 10 to print pitch 15, there result discontinuous vertical lines because the font of print pitch 15 is shorter than the font of print pitch 10 in the vertical direction. This is disadvantageous since such discontinuous vertical lines are usually not wanted.